Along with the recent development of small-sized and highly dense portable communication devices, personal computers, audio devices, and the like, small-sized and light weight electronic parts have been desired. The development of small-sized electronic parts has made the area of connecting terminals, such as terminal electrodes, small. Therefore, inferior connection tends to be caused, and a need has arisen to increase connection reliability.
As to connection reliability, it is desirable to improve the wettability of an electrode to a solder, and adhesive strength between a solder and an electrode. Conventionally, there has been a tendency to use electroless Ni/Au plating for the surface treatment of the electrode, to improve wettability to a solder. This electroless Ni/Au plating is accomplished by performing electroless Ni plating with phosphorous on an electrode terminal, and by further performing flash Au plating. Au on the surface layer prevents the oxidation of Ni in the under-layer during storage, and when connecting a solder the Au diffuses into the solder rapidly, thereby fresh Ni is exposed, exhibiting very high wettability to a solder.
However, the solder used here is an Sn—Pb solder, namely containing lead. It has been pointed out that machinery and tools using Sn—Pb solder after discarded are deteriorated by rain and snow, and by weathering, and give rise to soil and drinking-water pollution attributed to Pb components, with serious effects on the environment. For this, it is necessary to make haste in quickly change to electronic parts connected with a lead-free solder containing no lead.
In the case of an electroless Ni plating coat, connection is made using Sn—Pb/Ni. However, almost no studies have been done as to the connecting property between a lead-free solder and electroless Ni plating, because the electroless Ni plating coat has a short history, thus little developing in the connecting property.
Other and further features and advantages of the invention will appear more fully from the following description, taken in connection with the accompanying drawings.